This investigation is directed to characterization of the mechanism of the calcification process catalyzed by a collagenous matrix derived from mammalian tendon. The specific effects of selected inhibitors such as methylenediphosphonate, phosphonoacetate and tetracycline on net calcification, decalcification and on hypothetical intermediate calcium phosphate complex likely to be precursors of bound hydroxyapatite will be studied. The extent of binding of H3-tetracycline to amorphous calcium phosphate will be studied in an effort to evaluate if such an entity also constitutes one of the bound precursors. Since an amorphous form of calcium phosphate has also been implicated to be the product produced when calcium and phosphate are accumulated by isolated mitochondria, quantitative binding of tetracycline by rat liver and kidney mitochondria will also be studied by this technique. Studies will also be carried out to characterize a high molecular weight calcification inhibitor obtained by extraction of fresh beef tendon. The inhibitor will be purified and analyzed for its carbohydrate, protein, and lipid content and the effect of hydrolytic enzymes such as lysozyme, hyaluronidase, pepsin, trypsin and pronase on its inhibitory capacity will be determined. Studies will also be carried out to determine the presence of this inhibitor in other soft collagenous tissues, blood, and in the dialysate fluids derived from anephric patients.